Optical light engines using light emitting diodes offer considerable promise for a wide variety of applications. LED light engines integrate LED packaging with optical elements to provide maximum light output within a preselected illumination cone. Conventional LED light engines provide attractive alternatives to conventional halogen and incandescent bulbs in many applications, such as, for example, specialty illumination, display illumination, medical illumination and image projection.
One approach to fabricating LED light engines is to provide a base having a surface cavity, mounting one or more LED die in the cavity, and forming a lens structure encapsulating the LED die. FIG. 1 illustrates a light engine 10 produced according to the described process. As shown in FIG. 1, one or more LED die 11 are disposed on a base 12 within a surface cavity 13. The LED die 11 are electrically connected, using, for example, one or more bonding wires 16, and encapsulated in a lens of transparent material, such as an epoxy dome 14.
Unfortunately, the disposition of the LED die 11 in surface cavity 13 reduces the amount of light that can be extracted from the LED die 11. Since the LED die 11 emit light from each side, one or more walls 15 of the surface cavity 13 accept and absorb some of the side light emitted by each LED die 11, thus resulting in a reduction of the total flux emitted by the light engine 10. Moreover, the epoxy dome 14 is typically formed by injecting an epoxy into the cavity, using, for example, a syringe. This process, however, forms a dome having a hemispherical shape with a center that is typically spaced above the underlying LED die 11. Therefore, the LED die 11 is spaced away from the optimal center position, further reducing the efficiency of the light extraction.
One approach to increasing the extraction efficiency is to mount the LED die on a pedestal rising from the base, and to form a dome lens centered around the LED die. This approach has been implemented by placing a hollow plastic dome centered around a pedestal-mounted LED die and filling the plastic dome with silicone gel. A multi-step assembly process is required which includes the picking up and positioning of the hollow-dome, followed by the filling of the dome with silicone gel. This approach, however, is time-consuming and leads to increased manufacturing costs. Accordingly there is a need for an improved method of making an optical light engine including one or more elevated LED die.